The invention relates to a laser scanning apparatus, in particular for distance determination, having a transmitter unit which has a pulsed laser for the transmission of a light beam into a zone to be monitored, having a light deflection unit to deflect the light beam transmitted by the pulsed laser into the zone to be monitored, having a reception unit for the reception of light pulses which are reflected by an object located in the zone to be monitored and having a front screen which transmits the light beam and which separates the transmission unit, the reception unit and the light deflection unit from the surroundings of the laser scanning apparatus.
Such laser scanning apparatuses are generally known. They are used, for example, for distance determination in motor vehicles. The time between the transmission of a light pulse and the reception of the correspondingly reflected light pulse is measured and the distance between the laser scanning apparatus, i.e. the motor vehicle, and the object at which the light pulse was reflected is determined from the light speed and the run time of the received light pulse. In addition, such laser scanning apparatuses can be provided with a light deflection arrangement, for example a rotating light deflection arrangement to change the direction in which the light pulses are radiated within predetermined angular ranges. In this way, the surroundings of the laser scanning apparatus can be scanned within the predetermined ranges. The relative position of the object with respect to the laser scanning device can consequently be determined from the direction in which the light pulse was radiated and from the distance.
To ensure a reliable operation of the laser scanning apparatus, the light transmission, and thus the degree of contamination, of the front screen is monitored to ensure a uniform transmission and thus a correct range. For this purpose, a plurality of light sources, typically light-emitting diodes, and corresponding light detectors are usually arranged such that the light transmitted from the light sources passes through the front screen at least once on the way to the respective light detector. Deposits on the front screen which degrade or change the transmission of the front screen can be determined with reference to the intensity of the light detected by the light detector.
Moreover, the function of the transmission and reception unit is checked at regular time intervals. In laser scanning apparatuses which monitor an angular range of less than 360°, the light beam transmitted by the transmission unit is deflected for this purpose onto a reference target which is disposed on a side of the deflection device remote from the front screen, i.e. in a blind angular range, and reflects the light beam back onto the reception unit.
On a contamination of the front screen or on a disturbance in the transmission unit and/or the reception unit, a warning signal can be triggered.